1. Field of the Invention
The present invention relates to a fuel injection system for an internal combustion engine in which fuel is separately injected into each cylinder in turn in accordance with the firing order of the engine.
2. Description of the Prior Art
In known fuel injection systems for internal combustion engines of the above type, the main computing means for determining the timing and duration of the opening of the electromagnetically operated fuel injections valves, i.e., the timing of the fuel and the time duration of the injection are of the monostable circuit type which accomplishes the charging and discharging of electric energy in accordance with the engine rotational angle reference signals (the engine crankshaft rotational angle reference signals) and the air volume signals. A disadvantage of this type of fuel injection systems is that in the case of the four-cylinder engine operating at high speeds (under high speed, high load operating conditions), for example, the interval between the pulse signals generated from the monostable circuit becomes longer than that of the rotational angle reference signals (four pulses are generated for every one complete engine revolution) so that in order to separately inject fuel into each cylinder in turn in accordance with their firing order, the main computing means including the monostable circuit must be provided for each of the cylinders thus making the fuel injection system expensive to manufacture and complicate in construction. Another disadvantage is that if the valve opening area of the fuel injection valves is increased to decrease the duration of the opening of the fuel injection valves and thereby to eliminate the necessity of providing the main computing means for each of the cylinders, voltage and temperature changes result in unstable operation of the fuel injection valves and thus the controls which meet the requirements cannot be accomplished.